1. Field of the Invention
This invention relates to a method and apparatus for artificially and electrically stimulating cough reflex for improving the life span of individuals with higher level spinal cord injuries, and perhaps other individuals with impaired cough. This invention is a neural prosthetic apparatus and method for artificially restoring the ability to volitionally cough in a higher level spinal cord injured individual.
2. Description of Prior Art
Pulmonary complications presently account for the majority of morbidity and morality of spinal cord injured individuals. Polatty, R. Crystal, M. D. et al., Pulmonary Complications in the Spinal Cord Injury Patient, Physical Medicine and Rehabilitation, Vol. 1, No. 3, p. 353-373, August 1987; and Reines, H. David, M. D. et al., Pulmonary Complications of Acute Spinal Cord Injuries, Neurosurgery, Vol. 21, No. 2, p. 193-196, 1987. Two elements contribute to the high incidence of pulmonary morbidity in patients with acute spinal cord injuries. First, there is a restrictive effect of spinal cord injury on pulmonary function, and second, there is morbidity associated with immobilization required in the management of these injuries as well as the diminished active mobility. Retention of secretions, atelectasis, and pneumonia are the most commonly occurring complications and can lead to premature death.
Individuals with cervical spinal cord injuries are frequently impaired in their ability to cough. This deficit has traditionally been approached with the conventional assistive cough that requires physical assistance from a caregiver. Kirby, Nell A., R.N. et al., An Evaluation of Assisted Cough in Quadriparetic Patients, Archives of Physical Medicine & Rehabilitation, Vol. 47, p. 705-710, 1966; and Braun, Sheldon R., M.D. et al., Improving the Cough in Patients with Spinal Cord Injury, American Journal of Physical Medicine, Vol. 63, No. 1p. 1-10, 1984. It is likely that under these circumstances, the frequency of coughing in these individuals is reduced, Inability to cough is primarily due to paralysis of abdominal muscles.
This invention for cough assist should not be confused with conventional apparatuses or methods for phrenic pacing. Phrenic pacing is intended to cause contraction of the diaphragm, the major muscle of inspiration. The method and apparatus of this invention causes contraction of the major muscles of expiration, such as abdominal muscles. Phrenic pacing requires an invasive procedure, Glenn, William W. L. et al., Twenty Years of Experience in Phrenic Nerve Stimulation to Pace the Diaphragm, Pace, Vol. 9, p. 780-784, November-December 1986, Part I, although percutaneous alternatives, Peterson, D. K. et al, Intramuscular Electrical Activation of the Phrenic Nerve, IEEE Transactions on Biomedical Engineering, Vol. BME-33, No. 3, p. 342-351, March 1986, and surface alternatives, Geddes, L. A. et al., Electroventilation, American Journal of Emerg. Med., Vol. 3(4), p. 337-339, July 1985, have been proposed. One preferred embodiment of this invention is based on surface electrodes. Depending upon the success or problems with clinical application, a percutaneous or implant system may also be an effective way of stimulating the abdominal muscles for cough assist. Phrenic pacing and artificially stimulated cough reflex address two distinct problems, ventilation and coughing, respectively.
Linder, U.S. Pat. No. 5,190,036, discloses a method and apparatus for stimulating coughing in quadriplegic patients wherein an electrode belt is attached to an abdomen of a patient. At least one electrode of the belt is positioned in close contact with the abdominal area beneath the xiphoid process and costal margins of the patient. A pushbutton switch is momentarily depressed to activate a pulse generator and stimulus pulse circuit. Stimulus pulses are directed from the stimulus pulse circuit to the electrode while the patient is exhaling, so that an electrical stimulus is delivered to the abdominal area of the patient thereby increasing intrathoracic pressures to produce coughing by the patient. The pulse trains are of specified duration and frequency and have specified amplitudes and pulse widths. U.S. Pat. No. 5,190,036 does not teach or suggest an apparatus or method that alerts the patient of an upcoming cough so that the patient can coordinate a volitional activity, particularly after an adjustable time delay, in order to assist the apparatus and thus complete the cough. Furthermore, U.S. Pat. No. 5,190,036 does not teach or even suggest sensing and computing, as a function of a physical and temporal status of a cough and as a function of the current volitional activity of the user, an optimal time for producing a pulse electrical voltage to maximize an air flow rate of the cough.
There is an apparent need for an apparatus and method that enables a quadriplegic patient to initiate an artificially stimulated cough reflex and then to coordinate a volitional activity to complete the cough.